docs: def _make_matchers(self, crontab):
          '''
          This constructs the full matcher struct.
          '''
          crontab = _aliases.get(crontab, crontab)
          ct = crontab.split()
          if len(ct) == 5:
              ct.insert(0, '0')
              ct.append('*')
          elif len(ct) == 6:
              ct.insert(0, '0')
          _assert(len(ct) == 7,
              "improper number of cron entries specified; got %i need 5 to 7"%(len(ct,)))
  
          matchers = [_Matcher(which, entry) for which, entry in enumerate(ct)]
  
          return Matcher(*matchers)